The present disclosure generally relates to a photovoltaic thermal (PVT) system, and particularly to a photovoltaic thermal system configured to restore the electrical output efficiency of a photovoltaic thermal cell through a thermal anneal, and a method of operating the photovoltaic thermal system.
A photovoltaic cell is a device that converts light directly into electricity by the photovoltaic effect. Assemblies of photovoltaic cells are used to make solar panels, solar modules, or photovoltaic arrays. A photovoltaic cell can be formed by providing a large area p-n junction in a semiconductor material.
A photovoltaic thermal (PVT) cell employing a thin film of amorphous silicon material is capable of generating thermal output in addition to electricity because the amorphous silicon material heats up significantly during exposure to radiation, which can be solar radiation. The electrical output efficiency, i.e., the efficiency of the electrical output excluding the thermal output, of a photovoltaic thermal cell employing an amorphous silicon material can be enhanced by hydrogenating the amorphous silicon material. The electrical output efficiency of such a photovoltaic thermal cell degrades in time, however, with the light soaking time, i.e., the time of exposure to radiation. For example, the electrical output efficiency of a photovoltaic thermal cell can decrease by about 10% within 3-4 hours from the maximum electrical output efficiency. The loss in the electrical output efficiency of a photovoltaic thermal cell employing a thin film of amorphous silicon material can eventually saturate at about 20% after about 60 hours of operation.
However, it is necessary to alleviate or circumvent the loss in the electrical output efficiency in a photovoltaic thermal cell in order to improve economic viability of the photovoltaic thermal cell.